This invention relates to a method for increasing the texturing speeds of false-twist, draw-texturing processes such that the throughput of yarn can be enhanced by a factor of two or more times that previously obtainable by conventional draw-twisting texturing means. More particularly, the invention is directed to the production of false twist textured polyester continuous filament yarn at substantially increased throughput speeds without sacrifice of yarn properties, particularly yarn twist levels and bulk, and without the requirement of increased heat setting lengths.
In recent years, it has been recognized that false-twist texturing processes can be substantially improved both economically and in quality by combining the steps of drawing which were previously conventionally done by fiber manufacturers and the steps of twisting and heat setting the yarn in the twisted state. This latter step, known as texturing, was conventionally done by persons other than the fiber producer, i.e. throwsters. In combining the two steps, it has been found that not only has the previous separate drawing step been eliminated, but also improvements in textured yarn uniformity are realized.
Draw-texturing, however, has certain mechanical factors which physically limit the speed at which the yarn can pass through the texturing machinery. Practically all of the commercially operated false-twist texturing processes utilize what is known as spindle twisting to insert twist into the yarn which twist is heat set to produce the textured yarn. The twisting spindles must rotate once for every twist that is placed into the yarn and, thus, when the yarn is twisted at the relatively conventional rate of say 60 twists per inch, the spindle must rotate 60 times for every inch the yarn is forwarded through the apparatus. Thus, as a practical matter, the yarn forwarding speed through the apparatus is limited to approximately 650 to 675 feet per minute. Such a forwarding speed requires a spindle rotation at a speed approaching 500,000 revolutions per minute. At such speeds, the spindle has reached a speed wherein it becomes unstable and cannot be retained in the driven position with known spindle apparatuses. Additionally, there may well be a physical limit to the spindle speed based on the mass of the spindle which will limit the rotational speed to about that which can be achieved with present apparatuses.
A further factor in speed limitation is the heater length whereby the yarn is heat set in the twisted state. As the speed of the yarn increases, the residence time in a given length of heater means decreases. For a given yarn and temperature, however, the time required to bring the yarn to the heat setting temperature and set it does not change. In doubling the yarn throughput speed, it would be expected that the heater length zone would have to be at least lengthened, if not doubled. This, in fact, has been found to be the case with drawn and undrawn yarn. The consequent failure to increase the heater length zone results in a marked decrease in the bulk of the yarn so processed.
It is an object of the present invention to provide a method for overcoming the previous physical limitations in false twist texturing processing such that yarns can be processed at higher throughput speeds without increasing heater length and without reduction in the bulk of the yarn.
It is another object of the present invention to provide a process for false twist texturing yarns at speeds in excess of 850 feet per minute at twist levels of 54 or more twists per inch to produce yarns of comparable bulk and uniformity as previous methods.
It is a further object of the present invention to provide a process for producing higher bulk at comparable twist levels in polyester yarns.
These and other objects of the invention will become apparent from the description of the invention which follows.